Optimal selection of blended braking capacity for a hybrid electric vehicle

ABSTRACT

A hybrid powertrain system includes a transmission operative to transfer power between an input member and a torque machine and an output member coupled to a driveline coupled to a wheel including an actuable friction brake. The torque machine is operative to react torque transferred from the wheel through the driveline to the output member of the transmission. The torque machine is connected to an energy storage device. A method for operating a hybrid powertrain system includes monitoring an operator torque request input to an accelerator pedal, determining a minimum available power output of the energy storage device, determining a preferred output torque reacted through the output member to the driveline based upon the minimum available power output of the energy storage device, determining a regenerative braking torque capacity comprising a torque range between the preferred output torque reacted through the output member to the driveline and the operator torque request input to the accelerator pedal, and controlling operation of the hybrid powertrain based upon the regenerative braking torque capacity.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/985,248 filed on Nov. 4, 2007 which is hereby incorporated herein byreference.

TECHNICAL FIELD

This disclosure pertains to control systems for hybrid powertrainsystems.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Known hybrid powertrain architectures include torque-generative devices,including internal combustion engines and electric machines, whichtransfer torque through a transmission device to an output member. Oneexemplary hybrid powertrain includes a two-mode, compound-split,electro-mechanical transmission which utilizes an input member forreceiving tractive torque from a prime mover power source, preferably aninternal combustion engine, and an output member. The output member canbe operatively connected to a driveline for a motor vehicle fortransferring tractive torque thereto. Electric machines, operative asmotors or generators, generate a torque input to the transmission,independently of a torque input from the internal combustion engine. Theelectric machines may transform vehicle kinetic energy, transferredthrough the vehicle driveline, to electrical energy that is storable inan electrical energy storage device. A control system monitors variousinputs from the vehicle and the operator and provides operationalcontrol of the hybrid powertrain, including controlling transmissionoperating state and gear shifting, controlling the torque-generativedevices, and regulating the electrical power interchange among theelectrical energy storage device and the electric machines to manageoutputs of the transmission, including torque and rotational speed.

SUMMARY

A hybrid powertrain system includes a transmission operative to transferpower between an input member and a torque machine and an output membercoupled to a driveline coupled to a wheel including an actuable frictionbrake. The torque machine is operative to react torque transferred fromthe wheel through the driveline to the output member of thetransmission. The torque machine is connected to an energy storagedevice. A method for operating a hybrid powertrain system includesmonitoring an operator torque request input to an accelerator pedal,determining a minimum available power output of the energy storagedevice, determining a preferred output torque reacted through the outputmember to the driveline based upon the minimum available power output ofthe energy storage device, determining a regenerative braking torquecapacity comprising a torque range between the preferred output torquereacted through the output member to the driveline and the operatortorque request input to the accelerator pedal, and controlling operationof the hybrid powertrain based upon the regenerative braking torquecapacity.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an exemplary hybrid powertrain, inaccordance with the present disclosure;

FIG. 2 is a schematic diagram of an exemplary architecture for a controlsystem and hybrid powertrain, in accordance with the present disclosure;

FIGS. 3, 4, 5, and 6 are schematic flow diagrams of a control systemarchitecture for controlling and managing torque in a hybrid powertrainsystem, in accordance with the present disclosure; and

FIG. 7 is a datagraph, in accordance with the present disclosure.

DETAILED DESCRIPTION

Referring now to the drawings, wherein the showings are for the purposeof illustrating certain exemplary embodiments only and not for thepurpose of limiting the same, FIGS. 1 and 2 depict an exemplary hybridpowertrain. The exemplary hybrid powertrain in accordance with thepresent disclosure is depicted in FIG. 1, comprising a two-mode,compound-split, electromechanical hybrid transmission 10 operativelyconnected to an engine 4 and torque machines comprising first and secondelectric machines (‘MG-A’) 56 and (‘MG-B’) 72. The engine 14 and firstand second electric machines 56 and 72 each generate mechanical powerwhich can be transferred to the transmission 10. The power generated bythe engine 14 and the first and second electric machines 56 and 72 andtransferred to the transmission 10 is described in terms of input andmotor torques, referred to herein as T_(I), T_(A), and T_(B)respectively, and speed, referred to herein as N_(I), N_(A), and N_(B),respectively.

The exemplary engine 14 comprises a multi-cylinder internal combustionengine selectively operative in several states to transfer torque to thetransmission 10 via an input shaft 12, and can be either aspark-ignition or a compression-ignition engine. The engine 14 includesa crankshaft (not shown) operatively coupled to the input shaft 12 ofthe transmission 10. A rotational speed sensor 11 monitors rotationalspeed of the input shaft 12. Power output from the engine 14, comprisingrotational speed and engine torque, can differ from the input speedN_(I) and the input torque T_(I) to the transmission 10 due to placementof torque-consuming components on the input shaft 12 between the engine14 and the transmission 10, e.g., a hydraulic pump (not shown) and/or atorque management device (not shown).

The exemplary transmission 10 comprises three planetary-gear sets 24, 26and 28, and four selectively engageable torque-transferring devices,i.e., clutches C1 70, C2 62, C3 73, and C4 75. As used herein, clutchesrefer to any type of friction torque transfer device including single orcompound plate clutches or packs, band clutches, and brakes, forexample. A hydraulic control circuit 42, preferably controlled by atransmission control module (hereafter ‘TCM’) 17, is operative tocontrol clutch states. Clutches C2 62 and C4 75 preferably comprisehydraulically-applied rotating friction clutches. Clutches Cl 70 and C373 preferably comprise hydraulically-controlled stationary devices thatcan be selectively grounded to a transmission case 68. Each of theclutches C1 70, C2 62, C3 73, and C4 75 is preferably hydraulicallyapplied, selectively receiving pressurized hydraulic fluid via thehydraulic control circuit 42.

The first and second electric machines 56 and 72 preferably comprisethree-phase AC machines, each including a stator (not shown) and a rotor(not shown), and respective resolvers 80 and 82. The motor stator foreach machine is grounded to an outer portion of the transmission case68, and includes a stator core with coiled electrical windings extendingtherefrom. The rotor for the first electric machine 56 is supported on ahub plate gear that is operatively attached to shaft 60 via the secondplanetary gear set 26. The rotor for the second electric machine 72 isfixedly attached to a sleeve shaft hub 66.

Each of the resolvers 80 and 82 preferably comprises a variablereluctance device including a resolver stator (not shown) and a resolverrotor (not shown). The resolvers 80 and 82 are appropriately positionedand assembled on respective ones of the first and second electricmachines 56 and 72. Stators of respective ones of the resolvers 80 and82 are operatively connected to one of the stators for the first andsecond electric machines 56 and 72. The resolver rotors are operativelyconnected to the rotor for the corresponding first and second electricmachines 56 and 72. Each of the resolvers 80 and 82 is signally andoperatively connected to a transmission power inverter control module(hereafter ‘TPIM’) 19, and each senses and monitors rotational positionof the resolver rotor relative to the resolver stator, thus monitoringrotational position of respective ones of first and second electricmachines 56 and 72. Additionally, the signals output from the resolvers80 and 82 are interpreted to provide the rotational speeds for first andsecond electric machines 56 and 72, i.e., N_(A) and N_(B), respectively.

The transmission 10 includes an output member 64, e.g. a shaft, which isoperably connected to a driveline 90 for a vehicle (not shown), toprovide output power to the driveline 90 that is transferred to vehiclewheels 93, one of which is shown in FIG. 1. The output power at theoutput member 64 is characterized in terms of an output rotational speedN_(O) and an output torque T_(O). A transmission output speed sensor 84monitors rotational speed and rotational direction of the output member64. Each of the vehicle wheels 93 is preferably equipped with a sensor94 adapted to monitor wheel speed, the output of which is monitored by acontrol module of a distributed control module system described withrespect to FIG. 2, to determine vehicle speed, and absolute and relativewheel speeds for braking control, traction control, and vehicleacceleration management.

The input torque from the engine 14 and the motor torques from the firstand second electric machines 56 and 72 (T_(I), T_(A), and T_(B)respectively) are generated as a result of energy conversion from fuelor electrical potential stored in an electrical energy storage device(hereafter ‘ESD’) 74. The ESD 74 is high voltage DC-coupled to the TPIM19 via DC transfer conductors 27. The transfer conductors 27 include acontactor switch 38. When the contactor switch 38 is closed, undernormal operation, electric current can flow between the ESD 74 and theTPIM 19. When the contactor switch 38 is opened electric current flowbetween the ESD 74 and the TPIM 19 is interrupted. The TPIM 19 transmitselectrical power to and from the first electric machine 56 by transferconductors 29, and the TPIM 19 similarly transmits electrical power toand from the second electric machine 72 by transfer conductors 31 tomeet the torque commands for the first and second electric machines 56and 72 in response to the motor torques T_(A) and T_(B). Electricalcurrent is transmitted to and from the ESD 74 in accordance with whetherthe ESD 74 is being charged or discharged.

The TPIM 19 includes the pair of power inverters (not shown) andrespective motor control modules (not shown) configured to receive thetorque commands and control inverter states therefrom for providingmotor drive or regeneration functionality to meet the commanded motortorques T_(A) and T_(B). The power inverters comprise knowncomplementary three-phase power electronics devices, and each includes aplurality of insulated gate bipolar transistors (not shown) forconverting DC power from the ESD 74 to AC power for powering respectiveones of the first and second electric machines 56 and 72, by switchingat high frequencies. The insulated gate bipolar transistors form aswitch mode power supply configured to receive control commands. Thereis typically one pair of insulated gate bipolar transistors for eachphase of each of the three-phase electric machines. States of theinsulated gate bipolar transistors are controlled to provide motor drivemechanical power generation or electric power regenerationfunctionality. The three-phase inverters receive or supply DC electricpower via DC transfer conductors 27 and transform it to or fromthree-phase AC power, which is conducted to or from the first and secondelectric machines 56 and 72 for operation as motors or generators viatransfer conductors 29 and 31 respectively.

FIG. 2 is a schematic block diagram of the distributed control modulesystem. The elements described hereinafter comprise a subset of anoverall vehicle control architecture, and provide coordinated systemcontrol of the exemplary hybrid powertrain described in FIG. 1. Thedistributed control module system synthesizes pertinent information andinputs, and executes algorithms to control various actuators to meetcontrol objectives, including objectives related to fuel economy,emissions, performance, drivability, and protection of hardware,including batteries of ESD 74 and the first and second electric machines56 and 72. The distributed control module system includes an enginecontrol module (hereafter ‘ECM’) 23, the TCM 17, a battery pack controlmodule (hereafter ‘BPCM’) 21, and the TPIM 19. A hybrid control module(hereafter ‘HCP’) 5 provides supervisory control and coordination of theECM 23, the TCM 17, the BPCM 21, and the TPIM 19. A user interface(‘UI’) 13 is operatively connected to a plurality of devices throughwhich a vehicle operator controls or directs operation of theelectromechanical hybrid powertrain. The devices include an acceleratorpedal 113 (‘AP’), an operator brake pedal 112 (‘BP’), a transmissiongear selector 114 (‘PRNDL’), and a vehicle speed cruise control (notshown). The transmission gear selector 114 may have a discrete number ofoperator-selectable positions, including the rotational direction of theoutput member 64 to enable one of a forward and a reverse direction.

The aforementioned control modules communicate with other controlmodules, sensors, and actuators via a local area network (hereafter‘LAN’) bus 6. The LAN bus 6 allows for structured communication ofstates of operating parameters and actuator command signals between thevarious control modules. The specific communication protocol utilized isapplication-specific. The LAN bus 6 and appropriate protocols providefor robust messaging and multi-control module interfacing between theaforementioned control modules, and other control modules providingfunctionality including e.g., antilock braking, traction control, andvehicle stability. Multiple communications buses may be used to improvecommunications speed and provide some level of signal redundancy andintegrity. Communication between individual control modules can also beeffected using a direct link, e.g., a serial peripheral interface(‘SPI’) bus (not shown).

The HCP 5 provides supervisory control of the hybrid powertrain, servingto coordinate operation of the ECM 23, TCM 17, TPIM 19, and BPCM 21.Based upon various input signals from the user interface 13 and thehybrid powertrain, including the ESD 74, the HCP 5 determines anoperator torque request, an output torque command, an engine inputtorque command, clutch torque(s) for the applied torque-transferclutches C1 70, C2 62, C3 73, C4 75 of the transmission 10, and themotor torques T_(A) and T_(B) for the first and second electric machines56 and 72.

The ECM 23 is operatively connected to the engine 14, and functions toacquire data from sensors and control actuators of the engine 14 over aplurality of discrete lines, shown for simplicity as an aggregatebi-directional interface cable 35. The ECM 23 receives the engine inputtorque command from the HCP 5. The ECM 23 determines the actual engineinput torque, T_(I), provided to the transmission 10 at that point intime based upon monitored engine speed and load, which is communicatedto the HCP 5. The ECM 23 monitors input from the rotational speed sensor11 to determine the engine input speed to the input shaft 12, whichtranslates to the transmission input speed, N_(I). The ECM 23 monitorsinputs from sensors (not shown) to determine states of other engineoperating parameters including, e.g., a manifold pressure, enginecoolant temperature, ambient air temperature, and ambient pressure. Theengine load can be determined, for example, from the manifold pressure,or alternatiely, from monitoring operator input to the accelerator pedal113. The ECM 23 generates and communicates command signals to controlengine actuators, including, e.g., fuel injectors, ignition modules, andthrottle control modules, none of which are shown.

The TCM 17 is operatively connected to the transmission 10 and monitorsinputs from sensors (not shown) to determine states of transmissionoperating parameters. The TCM 17 generates and communicates commandsignals to control the transmission 10, including controlling thehydraulic control circuit 42. Inputs from the TCM 17 to the HCP 5include estimated clutch torques for each of the clutches, i.e., C1 70,C2 62, C3 73, and C4 75, and rotational output speed, NO, of the outputmember 64. Other actuators and sensors may be used to provide additionalinformation from the TCM 17 to the HCP 5 for control purposes. The TCM17 monitors inputs from pressure switches (not shown) and selectivelyactuates pressure control solenoids (not shown) and shift solenoids (notshown) of the hydraulic control circuit 42 to selectively actuate thevarious clutches C1 70, C2 62, C3 73, and C4 75 to achieve varioustransmission operating range states, as described hereinbelow.

The BPCM 21 is signally connected to sensors (not shown) to monitor theESD 74, including states of electrical current and voltage parameters,to provide information indicative of parametric states of the batteriesof the ESD 74 to the HCP 5. The parametric states of the batteriespreferably include battery state-of-charge, battery voltage, batterytemperature, and available battery power, referred to as a range P_(BAT)_(—) _(MIN) to P_(BAT) _(—) _(MAX).

A brake control module (hereafter ‘BrCM’) 22 is operatively connected tofriction brakes (not shown) on each of the vehicle wheels 93. The BrCM22 monitors the operator input to the brake pedal 112 and generatescontrol signals to control the friction brakes and sends a controlsignal to the HCP 5 to operate the first and second electric machines 56and 72 based thereon.

Each of the control modules ECM 23, TCM 17, TPIM 19, BPCM 21, and BrCM22 is preferably a general-purpose digital computer comprising amicroprocessor or central processing unit, storage mediums comprisingread only memory (‘ROM’), random access memory (‘RAM’), electricallyprogrammable read only memory (‘EPROM’), a high speed clock, analog todigital (‘A/D’) and digital to analog (‘D/A’) circuitry, andinput/output circuitry and devices (‘I/O’) and appropriate signalconditioning and buffer circuitry. Each of the control modules has a setof control algorithms, comprising resident program instructions andcalibrations stored in one of the storage mediums and executed toprovide the respective functions of each computer. Information transferbetween the control modules is preferably accomplished using the LAN bus6 and SPI buses. The control algorithms are executed during preset loopcycles such that each algorithm is executed at least once each loopcycle. Algorithms stored in the non-volatile memory devices are executedby one of the central processing units to monitor inputs from thesensing devices and execute control and diagnostic routines to controloperation of the actuators, using preset calibrations. Loop cycles areexecuted at regular intervals, for example each 3.125, 6.25, 12.5, 25and 100 milliseconds during ongoing operation of the hybrid powertrain.Alternatively, algorithms may be executed in response to the occurrenceof an event.

The exemplary hybrid powertrain selectively operates in one of severalstates that can be described in terms of engine states comprising one ofan engine-on state (‘ON’) and an engine-off state (‘OFF’), andtransmission operating range states comprising a plurality of fixedgears and continuously variable operating modes, described withreference to Table 1, below.

TABLE 1 Engine Transmission Operating Applied Description State RangeState Clutches M1_Eng_Off OFF EVT Mode 1 C1 70 M1_Eng_On ON EVT Mode 1C1 70 G1 ON Fixed Gear Ratio 1 C1 70 C4 75 G2 ON Fixed Gear Ratio 2 C170 C2 62 M2_Eng_Off OFF EVT Mode 2 C2 62 M2_Eng_On ON EVT Mode 2 C2 62G3 ON Fixed Gear Ratio 3 C2 62 C4 75 G4 ON Fixed Gear Ratio 4 C2 62 C373

Each of the transmission operating range states is described in thetable and indicates which of the specific clutches C1 70, C2 62, C3 73,and C4 75 are applied for each of the operating range states. A firstcontinuously variable mode, i.e., EVT Mode 1, or M1, is selected byapplying clutch C1 70 only in order to “ground” the outer gear member ofthe third planetary gear set 28. The engine state can be one of ON(‘M1_Eng_On’) or OFF (‘M1_Eng_Off’). A second continuously variablemode, i.e., EVT Mode 2, or M2, is selected by applying clutch C2 62 onlyto connect the shaft 60 to the carrier of the third planetary gear set28. The engine state can be one of ON (‘M2_Eng_On’) or OFF(‘M2_Eng_Off’). For purposes of this description, when the engine stateis OFF, the engine input speed is equal to zero revolutions per minute(‘RPM’), i.e., the engine crankshaft is not rotating. A fixed gearoperation provides a fixed ratio operation of input-to-output speed ofthe transmission 10, i.e., N_(I)/N_(O). A first fixed gear operation(‘G1’) is selected by applying clutches C1 70 and C4 75. A second fixedgear operation (‘G2’) is selected by applying clutches C1 70 and C2 62.A third fixed gear operation (‘G3’) is selected by applying clutches C262 and C4 75. A fourth fixed gear operation (‘G4’) is selected byapplying clutches C2 62 and C3 73. The fixed ratio operation ofinput-to-output speed increases with increased fixed gear operation dueto decreased gear ratios in the planetary gears 24, 26, and 28. Therotational speeds of the first and second electric machines 56 and 72,N_(A) and N_(B) respectively, are dependent on internal rotation of themechanism as defined by the clutching and are proportional to the inputspeed measured at the input shaft 12.

In response to operator input via the accelerator pedal 113 and brakepedal 112 as captured by the user interface 13, the HCP 5 and one ormore of the other control modules determine torque commands to controlthe torque generative devices comprising the engine 14 and the first andsecond electric machines 56 and 72 to meet the operator torque requestat the output member 64 and transferred to the driveline 90. Based uponinput signals from the user interface 13 and the hybrid powertrainincluding the ESD 74, the HCP 5 determines the operator torque request,a commanded output torque from the transmission 10 to the driveline 90,an input torque from the engine 14, clutch torques for thetorque-transfer clutches C1 70, C2 62, C3 73, C4 75 of the transmission10; and the motor torques for the first and second electric machines 56and 72, respectively, as is described hereinbelow.

Final vehicle acceleration can be affected by other factors including,e.g., road load, road grade, and vehicle mass. The engine state and thetransmission operating range state are determined based upon a varietyof operating characteristics of the hybrid powertrain. This includes theoperator torque request communicated through the accelerator pedal 113and brake pedal 112 to the user interface 13 as previously described.The transmission operating range state and the engine state may bepredicated on a hybrid powertrain torque demand caused by a command tooperate the first and second electric machines 56 and 72 in anelectrical energy generating mode or in a torque generating mode. Thetransmission operating range state and the engine state can bedetermined by an optimization algorithm or routine which determinesoptimum system efficiency based upon operator demand for power, batterystate of charge, and energy efficiencies of the engine 14 and the firstand second electric machines 56 and 72. The control system managestorque inputs from the engine 14 and the first and second electricmachines 56 and 72 based upon an outcome of the executed optimizationroutine, and system efficiencies are optimized thereby, to manage fueleconomy and battery charging. Furthermore, operation can be determinedbased upon a fault in a component or system. The HCP 5 monitors thetorque-generative devices, and determines the power output from thetransmission 10 at output member 64 that is required to meet theoperator torque request while meeting other powertrain operatingdemands, e.g., charging the ESD 74. As should be apparent from thedescription above, the ESD 74 and the first and second electric machines56 and 72 are electrically-operatively coupled for power flowtherebetween. Furthermore, the engine 14, the first and second electricmachines 56 and 72, and the electromechanical transmission 10 aremechanically-operatively coupled to transfer power therebetween togenerate a power flow to the output member 64.

FIG. 3 shows a control system architecture for controlling and managingsignal flow in a hybrid powertrain system having multiple torquegenerative devices, described hereinbelow with reference to the hybridpowertrain system of FIGS. 1 and 2, and residing in the aforementionedcontrol modules in the form of executable algorithms and calibrations.The control system architecture is applicable to alternative hybridpowertrain systems having multiple torque generative devices, including,e.g., a hybrid powertrain system having an engine and a single electricmachine, a hybrid powertrain system having an engine and multipleelectric machines. Alternatively, the hybrid powertrain system canutilize non-electric torque machines and energy storage systems, e.g.,hydraulic-mechanical hybrid transmissions using hydraulically poweredtorque machines (not shown).

In operation, the operator inputs to the accelerator pedal 113 and thebrake pedal 112 are monitored to determine the operator torque request.The operator inputs to the accelerator pedal 113 and the brake pedal 112comprise individually determinable operator torque request inputsincluding an immediate accelerator output torque request (‘Output TorqueRequest Accel Immed’), a predicted accelerator output torque request(‘Output Torque Request Accel Prdtd’), an immediate brake output torquerequest (‘Output Torque Request Brake Immed’), a predicted brake outputtorque request (‘Output Torque Request Brake Prdtd’) and an axle torqueresponse type (‘Axle Torque Response Type’). As used herein, the term‘accelerator’ refers to an operator request for forward propulsionpreferably resulting in increasing vehicle speed over the presentvehicle speed, when the operator selected position of the transmissiongear selector 114 commands operation of the vehicle in the forwarddirection. The terms ‘deceleration’ and ‘brake’ refer to an operatorrequest preferably resulting in decreasing vehicle speed from thepresent vehicle speed. The immediate accelerator output torque request,the predicted accelerator output torque request, the immediate brakeoutput torque request, the predicted brake output torque request, andthe axle torque response type are individual inputs to the controlsystem. Additionally, operation of the engine 14 and the transmission 10are monitored to determine the input speed (‘Ni’) and the output speed(‘No’).

The immediate accelerator output torque request comprises an immediatetorque request determined based upon the operator input to theaccelerator pedal 1 13. The control system controls the output torquefrom the hybrid powertrain system in response to the immediateaccelerator output torque request to cause positive acceleration of thevehicle. The immediate brake output torque request comprises animmediate braking request determined based upon the operator input tothe brake pedal 112. The control system controls the output torque fromthe hybrid powertrain system in response to the immediate brake outputtorque request to cause deceleration, or negative acceleration, of thevehicle. Vehicle deceleration effected by control of the output torquefrom the hybrid powertrain system is combined with vehicle decelerationeffected by a vehicle braking system (not shown) to decelerate thevehicle to achieve the immediate braking request.

The immediate accelerator output torque request is determined based upona presently occurring operator input to the accelerator pedal 113, andcomprises a request to generate an immediate output torque at the outputmember 64 preferably to accelerate the vehicle. The immediateaccelerator output torque request is unshaped, but can be shaped byevents that affect vehicle operation outside the powertrain control.Such events include vehicle level interruptions in the powertraincontrol for antilock braking, traction control and vehicle stabilitycontrol, which can be used to unshape or rate-limit the immediateaccelerator output torque request.

The predicted accelerator output torque request is determined based uponthe operator input to the accelerator pedal 113 and comprises an optimumor preferred output torque at the output member 64. The predictedaccelerator output torque request is preferably equal to the immediateaccelerator output torque request during normal operating conditions,e.g., when any one of antilock braking, traction control, or vehiclestability is not being commanded. When any one of antilock braking,traction control or vehicle stability is being commanded the predictedaccelerator output torque request remains the preferred output torquewith the immediate accelerator output torque request being decreased inresponse to output torque commands related to the antilock braking,traction control, or vehicle stability control.

The immediate brake output torque request is determined based upon theoperator input to the brake pedal 112 and the control signal to controlthe friction brakes to generate friction braking torque.

The predicted brake output torque request comprises an optimum orpreferred brake output torque at the output member 64 in response to anoperator input to the brake pedal 112 subject to a maximum brake outputtorque generated at the output member 64 allowable regardless of theoperator input to the brake pedal 112. In one embodiment the maximumbrake output torque generated at the output member 64 is limited to −0.2g. The predicted brake output torque request can be phased out to zerowhen vehicle speed approaches zero regardless of the operator input tothe brake pedal 112. As desired by a user, there can be operatingconditions under which the predicted brake output torque request is setto zero, e.g., when the operator setting to the transmission gearselector 114 is set to a reverse gear, and when a transfer case (notshown) is set to a four-wheel drive low range. The operating conditionswhereat the predicted brake output torque request is set to zero arethose in which blended braking is not preferred due to vehicle operatingfactors.

The axle torque response type comprises an input state for shaping andrate-limiting the output torque response through the first and secondelectric machines 56 and 72. The input state for the axle torqueresponse type can be an active state, preferably comprising one of apleasability limited state a maximum range state, and an inactive state.When the commanded axle torque response type is the active state, theoutput torque command is the immediate output torque. Preferably thetorque response for this response type is as fast as possible.

Blended brake torque includes a combination of the friction brakingtorque generated at the wheels 93 and the output torque generated at theoutput member 64 which reacts with the driveline 90 to decelerate thevehicle in response to the operator input to the brake pedal 112. TheBrCM 22 commands the friction brakes on the wheels 93 to apply brakingforce and generates a command for the transmission 10 to create anegative output torque which reacts with the driveline 90 in response tothe immediate braking request. Preferably the applied braking force andthe negative output torque can decelerate and stop the vehicle so longas they are sufficient to overcome vehicle kinetic power at wheel(s) 93.The negative output torque reacts with the driveline 90, thustransferring torque to the electromechanical transmission 10 and theengine 14. The negative output torque reacted through theelectromechanical transmission 10 can be transferred to the first andsecond electric machines 56 and 72 to generate electric power forstorage in the ESD 74.

A strategic optimization control scheme (‘Strategic Control’) 310determines a preferred input speed (‘Ni_Des’) and a preferred enginestate and transmission operating range state (‘Hybrid Range State Des’)based upon the output speed and the operator torque request and basedupon other operating parameters of the hybrid powertrain, includingbattery power limits and response limits of the engine 14, thetransmission 10, and the first and second electric machines 56 and 72.The predicted accelerator output torque request and the predicted brakeoutput torque request are input to the strategic optimization controlscheme 310. The strategic optimization control scheme 310 is preferablyexecuted by the HCP 5 during each 100 ms loop cycle and each 25 ms loopcycle. The desired operating range state for the transmission 10 and thedesired input speed from the engine 14 to the transmission 10 are inputsto the shift execution and engine start/stop control scheme 320.

The shift execution and engine start/stop control scheme 320 commandschanges in the transmission operation (‘Transmission Commands’)including changing the operating range state based upon the inputs andoperation of the powertrain system. This includes commanding executionof a change in the transmission operating range state if the preferredoperating range state is different from the present operating rangestate by commanding changes in application of one or more of theclutches C1 70, C2 62, C3 73, and C4 75 and other transmission commands.The present operating range state (‘Hybrid Range State Actual’) and aninput speed profile (‘Ni_Prof’) can be determined. The input speedprofile is an estimate of an upcoming input speed and preferablycomprises a scalar parametric value that is a targeted input speed forthe forthcoming loop cycle. The engine operating commands and theoperator torque request are based upon the input speed profile during atransition in the operating range state of the transmission.

A tactical control scheme (‘Tactical Control and Operation’) 330 isrepeatedly executed during one of the control loop cycles to determineengine commands (‘Engine Commands’) for operating the engine 14,including a preferred input torque from the engine 14 to thetransmission 10 based upon the output speed, the input speed, and theoperator torque request comprising the immediate accelerator outputtorque request, the predicted accelerator output torque request, theimmediate brake output torque request, the predicted brake output torquerequest, the axle torque response type, and the present operating rangestate for the transmission. The engine commands also include enginestates including one of an all-cylinder operating state and a cylinderdeactivation operating state wherein a portion of the engine cylindersare deactivated and unfueled, and engine states including one of afueled state and a fuel cutoff state. An engine command comprising thepreferred input torque of the engine 14 and a present input torque(‘Ti’) reacting between the engine 14 and the input member 12 arepreferably determined in the ECM 23. Clutch torques (‘Tcl’) for each ofthe clutches C1 70, C2 62, C3 73, and C4 75, including the presentlyapplied clutches and the non-applied clutches are estimated, preferablyin the TCM 17.

An output and motor torque determination scheme (‘Output and MotorTorque Determination’) 340 is executed to determine the preferred outputtorque from the powertrain (‘To_cmd’). This includes determining motortorque commands (‘T_(A)’, ‘T_(B)’) to transfer a net commanded outputtorque to the output member 64 of the transmission 10 that meets theoperator torque request, by controlling the first and second electricmachines 56 and 72 in this embodiment. The immediate accelerator outputtorque request, the immediate brake output torque request, the presentinput torque from the engine 14 and the estimated applied clutchtorque(s), the present operating range state of the transmission 10, theinput speed, the input speed profile, and the axle torque response typeare inputs. The output and motor torque determination scheme 340executes to determine the motor torque commands during each iteration ofone of the loop cycles. The output and motor torque determination scheme340 includes algorithmic code which is regularly executed during the6.25 ms and 12.5 ms loop cycles to determine the preferred motor torquecommands.

The hybrid powertrain is controlled to transfer the output torque to theoutput member 64 to the driveline 90 to generate tractive torque atwheel(s) 93 to forwardly propel the vehicle in response to the operatorinput to the accelerator pedal 113 when the operator selected positionof the transmission gear selector 114 commands operation of the vehiclein the forward direction. Similarly, the hybrid powertrain is controlledto transfer the output torque to the output member 64 to the driveline90 to generate tractive torque at wheel(s) 93 to propel the vehicle in areverse direction in response to the operator input to the acceleratorpedal 113 when the operator selected position of the transmission gearselector 114 commands operation of the vehicle in the reverse direction.Preferably, propelling the vehicle results in vehicle acceleration solong as the output torque is sufficient to overcome external loads onthe vehicle, e.g., due to road grade, aerodynamic loads, and otherloads.

FIG. 4 details signal flow for the output and motor torque determinationscheme 340 for controlling and managing the output torque through thefirst and second electric machines 56 and 72, described with referenceto the hybrid powertrain system of FIGS. 1 and 2 and the control systemarchitecture of FIG. 3. The output and motor torque determination scheme340 controls the motor torque commands of the first and second electricmachines 56 and 72 to transfer a net output torque to the output member64 of the transmission 10 that reacts with the driveline 90 and meetsthe operator torque request, subject to constraints and shaping. Theoutput and motor torque determination scheme 340 preferably includesalgorithmic code and predetermined calibration code which is regularlyexecuted during the 6.25 ms and 12.5 ms loop cycles to determinepreferred motor torque commands (‘T_(A)’, ‘T_(B)’) for controlling thefirst and second electric machines 56 and 72 in this embodiment.

The output and motor torque determination scheme 340 determines and usesa plurality of inputs to determine constraints on the output torque,from which it determines the output torque command (‘To_cmd’). The motortorque commands (‘T_(A)’, ‘T_(B)’) for the first and second electricmachines 56 and 72 can be determined based upon the output torquecommand. The inputs to the output and motor torque determination scheme340 include operator inputs, powertrain system inputs and constraints,and autonomic control inputs.

The operator inputs include the immediate accelerator output torquerequest (‘Output Torque Request Accel Immed’) and the immediate brakeoutput torque request (‘Output Torque Request Brake Immed’).

The autonomic control inputs include torque offsets to effect activedamping of the driveline 90 (412), to effect engine pulse cancellation(408), and to effect a closed loop correction based upon the input andclutch slip speeds (410). The torque offsets for the first and secondelectric machines 56 and 72 to effect active damping of the driveline 90can be determined (‘Ta AD’, ‘Tb AD’), e.g., to manage and effectdriveline lash adjustment, and are output from an active dampingalgorithm (‘AD’) (412). The torque offsets to effect engine pulsecancellation (‘Ta PC’, ‘Tb PC’) are determined during starting andstopping of the engine during transitions between the engine-on state(‘ON’) and the engine-off state (‘OFF’) to cancel engine torquedisturbances in unfired cylinders, and are output from a pulsecancellation algorithm (‘PC’) (408). The torque offsets for the firstand second electric machines 56 and 72 to effect closed-loop correctiontorque are determined by monitoring input speed to the transmission 10and clutch slip speeds of clutches C1 70, C2 62, C3 73, and C4 75. Theclosed-loop correction torque offsets for the first and second electricmachines 56 and 72 (‘Ta CL’, ‘Tb CL’) can be determined based upon aninput speed error, i.e., a difference between the input speed (‘Ni’),e.g., as measured using sensor 11 or using the resolvers 80 and 82, andthe input speed profile (‘Ni Prof’) and a clutch slip speed error, i.e.,a difference between clutch slip speed and a targeted clutch slip speed,e.g., a clutch slip speed profile for a targeted clutch C1 70. Whenoperating in one of the mode operating range states, the closed-loopcorrection motor torque offsets for the first and second electricmachines 56 and 72 (‘Ta CL’, ‘Tb CL’) can be determined primarily basedupon the input speed error. When operating in Neutral, the closed-loopcorrection is based upon the input speed error and the clutch slip speederror for a targeted clutch, e.g., C1 70. The closed-loop correctionmotor torque offsets are output from a closed loop control algorithm(‘CL’) (410). The clutch slip speeds of the non-applied clutches can bedetermined for the specific operating range state based upon motorspeeds for the first and second electric machines 56 and 72 and thespeed of the output member 64. The targeted clutch slip speed and clutchslip profile are preferably used during a transition in the operatingrange state of the transmission to synchronize clutch slip speed priorto applying an oncoming clutch, and operating the powertrain at an idlecondition, in anticipation of a shift to a drive range. The closed-loopmotor torque offsets and the motor torque offsets to effect activedamping of the driveline 90 are input to a low pass filter to determinefiltered motor torque corrections for the first and second electricmachines 56 and 72 (‘Ta LPF’ and Tb LPF’) (405).

A general governing equation for determining the closed-loop correctiontorque offsets for the first and second electric machines 56 and 72 (‘TaCL’, ‘Tb CL’) for the exemplary transmission 10 is set forth in Eq. 1below:

$\begin{matrix}{\begin{bmatrix}{T_{I}{CL}} \\{T_{O}{CL}}\end{bmatrix} = {\lbrack A_{1} \rbrack \begin{bmatrix}{Ta} & {CL} \\{Tb} & {CL}\end{bmatrix}}} & \lbrack 1\rbrack\end{matrix}$

wherein A₁ is a 2×2 matrix containing system-specific scalar values. Arange of input torques, i.e., the minimum and maximum input torqueconstraints can be determined by executing the governing equation takinginto account the net immediate output torque and the immediateaccelerator output torque, the input and output member accelerations,and the clutch reactive torques. The powertrain system inputs andconstraints include maximum and minimum available battery power limits(‘P_(BAT) Min/Max’) output from a battery power limit algorithm(‘P_(BAT)’) (466), the operating range state (‘Hybrid Range State’), anda plurality of system inputs and constraints (‘System Inputs andConstraints’). The system inputs can include scalar parameters specificto the powertrain system and the operating range state, and can berelated to speed and acceleration of the input member 12, output member64, and the clutches. Other system inputs are related to systeminertias, damping, and electric/mechanical power conversion efficienciesin this embodiment. The constraints include maximum and minimum motortorque outputs from the torque machines, i.e., first and second electricmachines 56 and 72 and maximum and minimum clutch reactive torques forthe applied clutches. Other system inputs include the input torque,clutch slip speeds and other relevant states.

Inputs including an input acceleration profile (‘Nidot Prof’) and aclutch slip acceleration profile (“Clutch Slip Accel Prof”) are input toa pre-optimization algorithm (415), along with the system inputs, theoperating range state, and the motor torque corrections for the firstand second electric machines 56 and 72 (‘Ta LPF’ and Tb LPF’). The inputacceleration profile is an estimate of an upcoming input accelerationthat preferably comprises a targeted input acceleration for theforthcoming loop cycle. The clutch slip acceleration profile is anestimate of upcoming clutch acceleration for one or more of thenon-applied clutches, and preferably comprises a targeted clutch slipacceleration for the forthcoming loop cycle. Optimization inputs (‘OptInputs’), which can include values for motor torques, clutch torques andoutput torques can be calculated for the present operating range stateand used in an optimization algorithm (440). The optimization algorithm(440) is preferably executed to determine the maximum and minimum rawoutput torque constraints (440) and to determine the preferred split ofopen-loop torque commands between the first and second electric machines56 and 72 (440′). The optimization inputs, the maximum and minimumbattery power limits, the system inputs and the present operating rangestate are analyzed to determine a preferred or optimum output torque(‘To Opt’) and minimum and maximum raw output torque constraints (‘ToMin Raw’, ‘To Max Raw’) which can be shaped and filtered (420). Thepreferred output torque (‘To Opt’) comprises an output torque thatminimizes battery power subject to a range of net output torques thatare less than the immediate accelerator output torque request. Thepreferred output torque comprises the net output torque that is lessthan the immediate accelerator output torque request and yields theminimum battery power subject to the output torque constraints. Theimmediate accelerator output torque request and the immediate brakeoutput torque request are each shaped and filtered and subjected to theminimum and maximum output torque constraints (‘To Min Filt’, ‘To MaxFilt’) to determine minimum and maximum filtered output torque requestconstraints (‘To Min Req Filt’, ‘To Max Req Filt’). A constrainedaccelerator output torque request (‘To Req Accel Cnstrnd’) and aconstrained brake output torque request (‘To Req Brake Cnstrnd’) can bedetermined based upon the minimum and maximum filtered output torquerequest constraints (425). The constrained accelerator output torquerequest and the constrained brake output torque request comprise theimmediate accelerator output torque request and the immediate brakeoutput torque request limited within the maximum and minimum outputtorque constraints. Furthermore, a regenerative braking capacity (‘OptRegen Capacity’) of the transmission 10 comprises a capacity of thetransmission 10 to react driveline torque, and can be determined basedupon constraints including maximum and minimum motor torque outputs fromthe torque machines and maximum and minimum reactive torques for theapplied clutches, taking into account the battery power limits. Theregenerative braking capacity establishes a maximum value for theimmediate brake output torque request. The regenerative braking capacityis determined based upon a difference between the constrainedaccelerator output torque request and the preferred output torque (‘ToOpt’), shown with reference to FIG. 7. The constrained acceleratoroutput torque request is shaped and filtered and combined with aconstrained, shaped, and filtered brake output torque request todetermine a net output torque command. The net output torque command iscompared to the minimum and maximum request filtered output torques todetermine the output torque command (‘To_cmd’) (430). When the netoutput torque command is between the maximum and minimum requestfiltered output torques, the output torque command is set to the netoutput torque command. When the net output torque command exceeds themaximum request filtered output torque, the output torque command is setto the maximum request filtered output torque. When the net outputtorque command is less than the minimum request filtered output torque,the output torque command is set to the minimum request filtered outputtorque command.

Powertrain operation is monitored and combined with the output torquecommand to determine a preferred split of open-loop torque commandsbetween the first and second electric machines 56 and 72 that meetsreactive clutch torque capacities (‘Ta Opt’ and ‘Tb Opt’), and providefeedback related to the preferred battery power (‘Pbat Opt’) (440′). Theoutput torque search range (‘To Search Range’) preferably comprises theoutput torque command (‘To_cmd’) when the optimization algorithm (440)is used to determine the preferred split of open-loop torque commandsbetween the first and second electric machines 56 and 72 (440′). Themotor torque corrections for the first and second electric machines 56and 72 (‘Ta LPF’ and Tb LPF’) are subtracted to determine open loopmotor torque commands (‘Ta OL’ and ‘Tb OL’) (460).

The open loop motor torque commands are combined with the autonomiccontrol inputs including the torque offsets to effect active damping ofthe driveline 90 (412), to effect engine pulse cancellation (408), andto effect a closed loop correction based upon the input and clutch slipspeeds (410) and to determine the motor torques T_(A) and T_(B) forcontrolling the first and second electric machines 56 and 72 (470). Theaforementioned steps of constraining, shaping and filtering the outputtorque request to determine the output torque command which is convertedinto the motor torque commands for the first and second electricmachines 56 and 72 is preferably a feed-forward operation which actsupon the inputs and uses algorithmic code to calculate the torquecommands.

The system operation as configured leads to determining output torqueconstraints based upon present operation and constraints of thepowertrain system. The operator torque request is determined based uponoperator inputs to the brake pedal and to the accelerator pedal. Theoperator torque request can be constrained, shaped and filtered todetermine the output torque command, including determining a preferredregenerative braking capacity. An output torque command can bedetermined that is constrained based upon the constraints and theoperator torque request. The output torque command is implemented bycommanding operation of the torque machines. The system operationeffects powertrain operation that is responsive to the operator torquerequest and within system constraints. The system operation results inan output torque shaped with reference to operator driveability demands,including smooth operation during regenerative braking operation.

FIG. 5 schematically shows details of the optimization function 440which includes monitoring present operating conditions of theelectro-mechanical hybrid powertrain, e.g., the powertrain systemdescribed hereinabove. Offset motor torques for the first and secondelectric machines 56 and 72 can be calculated based upon inputsincluding the operating range state (‘ORS’) of the transmission 10, theinput torque (‘T_(I)’) and other terms based upon system inertias,system damping, and clutch slippage (510).

The control system executes an algorithm to determine linear torqueconstraints to the output torque (520). The linear torque constraintscomprise a plurality of system constraints that achieve a linear changein the output torque with a linear change in one of the constraints. Thesystem constraints describe a capability of the hybrid transmission 10to transfer and convert electric power to mechanical torque through thefirst and second electric machines 56 and 72. Inputs associated with thelinear torque constraints include motor torque constraints comprisingminimum and maximum achievable motor torques for the first and secondelectric machines 56 and 72 (‘T_(A)Min’, ‘T_(A)Max’, ‘T_(B)Min’, and‘T_(B)Max’), and minimum and maximum clutch reactive torques for appliedclutch(es) for first and where necessary, second applied clutches(‘T_(CLn)Min’, ‘T_(CLn)Max’) and immediate or present torque, speed, andelectric power inputs. Minimum and maximum linear output torques (‘ToMin Lin’, ‘To Max Lin’) can be determined based upon the minimum andmaximum achievable motor torques for the first and second electricmachines 56 and 72 and the minimum and maximum clutch reactive torquesfor the applied clutch(es). The minimum and maximum linear outputtorques are the minimum and maximum output torques that meet the motortorque constraints and also meet the applied clutch torque constraints.The minimum and maximum linear output torques (‘To Min Lin’, ‘To MaxLin’) translate to the minimum and maximum raw output torques (‘To MinRaw’, ‘To Max Raw’).

The control system executes an algorithm to determine quadratic torqueconstraints to the output torque (530). The quadratic torque constraintscomprise a plurality of system constraints that achieve a quadraticchange in the output torque with a linear change in one of theconstraints. Constraint inputs include the available battery power (notshown) for an exemplary system (530). The available battery power forthe energy storage device 74 can be represented mathematically as afunction of the transmission output torque To as shown in Eq. 2 below:

P _(BAT)(T _(O))=(a ² +b ₁ ²)(T _(O) −T _(O)*)² +P _(BAT)   [2]

wherein a₁ and b₁ represent scalar values determined for the specificapplication. Eq. 2 can be solved for the output torque, as shown in Eq.3 below.

$\begin{matrix}{{T_{O}( P_{BAT} )} = {T_{O}^{*} \pm \sqrt{\frac{P_{BAT} - P_{BAT}^{*}}{a_{1}^{2} + b_{1}^{2}}}}} & \lbrack 3\rbrack\end{matrix}$

For the available battery power range P_(BAT) _(—) _(MIN) to P_(BAT)_(—) _(MAX), four distinct output torques can be determined from Eq. 3,including maximum and minimum quadratic output torque constraints forthe positive root case and minimum and maximum quadratic output torqueconstraints for the negative root case (‘To@P_(BAT) Max’ and ‘To@P_(BAT)Min’), and represent achievable ranges for the output torque based uponthe battery power, depending on whether discharging, i.e., the positiveroot case, or charging, i.e., the negative root case.

The preferred output torque (‘To Opt’) can be determined based upon theoptimized output torque (‘To*’), the optimized battery power(‘P_(BAT)*’), the maximum and minimum linear output torques, the minimumand maximum quadratic output torque constraints (‘To@P_(BAT) Max’ and‘To@P_(BAT) Min’) selected based upon whether charging or discharging,and the output torque search range (‘To Search Range’). The outputtorque search range (‘To Search Range’) preferably comprises theimmediate accelerator output torque request (‘To_req’) when operating ina tractive torque generating state to forwardly propel the vehicle. Theoutput torque search range (‘To Search Range’) preferably comprises arange between the immediate accelerator output torque request and abrake torque request when operating in a regenerative braking state toslow the vehicle. Determining the preferred output torque can includeselecting a temporary output torque comprising a minimum torque value ofthe search range for the output torque and the maximum output torque.The preferred output torque (‘To Opt’) is selected as the maximum of thetemporary output torque, the minimum output torque determined based uponone of the quadratic output torque constraints and clutch torqueconstraints, and the minimum linear output torque (540). The preferredoutput torque (‘To Opt’) is determined based upon inputs including theimmediate accelerator output torque request. The preferred output torque(‘To Opt’) translates to the preferred output torque (‘To(j)’) outputfrom the optimization function 440.

The preferred output torque (‘To Opt’) is subject to output torqueconstraints comprising the minimum and maximum unfiltered output torques(‘To Min Raw’, ‘To Max Raw’) and is determined based upon the range ofallowable output torques, which can vary, and may comprise the immediateaccelerator output torque request. The preferred output torque maycomprise an output torque corresponding to a minimum battery dischargepower or an output torque corresponding to a maximum battery chargepower. The preferred output torque is based upon a capacity of thepowertrain to transmit and convert electric power to mechanical torquethrough the first and second electric machines 56 and 72, and theimmediate or present torque, speed, and reactive clutch torqueconstraints, and electric power inputs thereto. The output torqueconstraints including the minimum and maximum unfiltered output torques(‘To Min Raw’, ‘To Max Raw’) and the preferred output torque (‘To Opt’)can be determined by executing and solving an optimization function inone of the operating range states for neutral, mode and fixed gearoperation. The optimization function 440 comprises a plurality of linearequations implemented in an executable algorithm and solved duringongoing operation of the system to determine the preferred output torquerange to minimize battery power consumption and meet the operator torquerequest. Each of the linear equations takes into account the inputtorque (‘Ti’), system inertias and linear damping. Preferably, there arelinear equations specific to each of the operating range states forneutral, mode and fixed gear operations.

The output torque constraints comprise a preferred output torque rangeat the present input torque, within the available battery power andwithin the motor torque constraints subject to the reactive clutchtorques of the applied torque transfer clutches. The output torquecommand is constrained within maximum and minimum output torquecapacities. In fixed gear and mode operation, the preferred outputtorque can comprise the output torque which maximizes charging of theESD 74. In neutral, the preferred output torque is calculated. In fixedgear operation, the preferred output torque can include the preferredtorque split between the first and second electric machines 56 and 72while meeting the reactive clutch torque constraints.

Preferred motor torques and battery powers (‘T_(A) Opt’, ‘T_(B) Opt’,and ‘P_(BAT) Opt’) can be determined based upon the preferred outputtorque, and used to control operation of the powertrain system. Thepreferred motor torques comprise motor torques which minimize power flowfrom the ESD 74 and achieve the preferred output torque. Torque outputsfrom the first and second electric machines 56 and 72 are controlledbased upon the determined minimum power flow from the ESD 74, which isthe preferred battery power (‘P_(BAT) Opt’). Torque output is controlledbased upon the engine input torque and the motor torque commands for thefirst and second electric machines 56 and 72, (‘T_(A) Opt’, ‘T_(B) Opt’)respectively, which minimizes the power flow from the ESD 74 to meet thepreferred output torque. The battery powers associated with the motors(‘P_(A) Opt’ and ‘P_(B) Opt’, respectively) can be determined based uponthe torque commands (560).

The motor torque commands can be used to control the first and secondelectric machines 56 and 72 to transfer output torque to the outputmember 64 and thence to the driveline 90 to generate tractive torque atwheel(s) 93 to propel the vehicle in response to the operator input tothe accelerator pedal 113. Preferably, propelling the vehicle results invehicle acceleration so long as the output torque is sufficient toovercome external loads on the vehicle, e.g., due to road grade,aerodynamic loads, and other loads.

FIG. 6 shows a control system architecture for managing signal flow inthe distributed control system to control output torque includingtractive braking through one or more of the vehicle wheels 93, describedwith reference to the hybrid powertrain described hereinabove. The BrCM22 monitors the operator braking request input to the brake pedal 112(‘Operator Braking Request’), and determines a total braking torquerequest (‘Total Braking Torque Request’). The BrCM 22 generates aregenerative braking axle torque request (‘Regenerative Braking AxleTorque Request’) based upon the total braking torque request and aregenerative braking axle torque capacity (‘Regen Capacity’) and anypresently applied regenerative braking torque (‘Estimated Regen BrakingAchieved Torque’). The regenerative braking axle torque requestpreferably comprises the immediate brake output torque request describedhereinabove with reference to FIG. 3, scaled based upon axle ratio ofthe driveline 90 and filtered. The BrCM 22 generates a control signal(‘Friction Brake Control’) to control the actuable friction brake ineach of the wheels 93 based upon a difference between the operatorbraking request and the regenerative braking torque that can be reactedthrough the transmission 10 by operation of the first and secondelectric machines 56 and 72 as estimated by the HCP 5. The BrCM 22 actsas a master arbitrator for controlling the friction brakes and thetransmission 10 to meet the operator braking request.

The HCP 5 determines the regenerative braking axle torque capacity,which is a torque-based measurement of the ability of the transmission10 to react torque from the driveline 90 through the selectively appliedclutches C1 70, C2 62, C3 73, and C4 75 to the first and second electricmachines 56 and 72, limited by the maximum brake output torque scaledbased upon the axle ratio and filtered and rate-limited. Theregenerative braking axle torque capacity preferably comprises theregenerative braking capacity (‘Opt Regen Capacity’) of the transmission10 described herein with reference to FIG. 4. The HCP 5 estimates thepresently applied regenerative braking torque reacted from the driveline90 and the output member 64 of the transmission 10, and communicates theregenerative braking axle torque capacity and the regenerative brakingtorque to the BrCM 22. The HCP 5 determines the preferred output torquefrom the powertrain (‘To_cmd’) through the motor torque control scheme340 and generates the motor torque commands (‘T_(A)’, ‘T_(B)’) forcontrolling the first and second electric machines 56 and 72 based uponthe regenerative braking axle torque request utilizing the controlarchitecture described with reference to FIGS. 3 and 4.

The timing sequence of transmitting signals from the brake pedal 112 tothe BrCM 22 and subsequently to the HCP 5 is intentional, as the mostcurrently available operator input to the brake pedal can be used tocontrol braking during a braking event. The HCP 5 leverages recuperationof kinetic energy through regenerative braking to generate storableelectric power and improve operating efficiency.

The control system is described hereinabove with reference to anembodiment including the engine 14 and torque machines comprising thefirst and second electric machines 56 and 72 coupled to theelectromechanical transmission 10. Alternatively, the control system canbe used with other transmission systems having torque machines andenergy storage systems which can controllably react torque through adriveline to effect tractive braking, preferably those that use thereactive torque through the driveline to generate storable power forsubsequent use, e.g., in the form of stored electric power, storedhydraulic power, or stored mechanical power.

In operation, the operator torque request input to the accelerator pedal113 is monitored, and a minimum available power output of the ESD 74 canbe determined. A preferred output torque reacted through the outputmember 64 to the driveline 90 is determined based upon the minimumavailable power output of the energy storage device. The regenerativebraking torque capacity, comprising a torque range between the preferredoutput torque reacted through the output member to the driveline and theoperator torque request input to the accelerator pedal, can bedetermined. Preferably the immediate accelerator output torque requestis determined based upon the operator input to the accelerator pedal.Operator input to a brake pedal can also be monitored, and an immediatebrake output torque request is determined based upon the operator inputto the brake pedal during the operator brake request, thus commandingoperation of the powertrain system based upon the operator torquerequest including the operator brake.

The operation of the transmission 10 can include commanding a shift fromone of the fixed gears, e.g., G1, G2, G3, and G4. The shift operationpreferably includes initially transitioning to operating in one of thecontinuously variable operating range states, e.g., M1 and M2. Theoperation of the powertrain is controlled during operation in thecontinuously variable operating range state, including controllingreacted output torque from the transmission 10 based upon theregenerative braking torque capacity.

Therefore, operation of the engine 14 can be managed through thetactical operation 330, and the output and motor determination scheme340 can manage motor torques of the first and second electric machines56 and 72. This operation includes determining the preferred outputtorque reacted through the output member 64 to the driveline 90 basedupon the minimum available power output of the energy storage device andclutch reactive torque for the selectively applied torque transferclutches. This operation can be important when the torque constraintsare such that the optimized output torque (‘To*’) and the optimizedbattery power (‘P_(BAT)*’) determined with reference to Eqs. 1 and 2,above, fall within the minimum and maximum linear output torques (‘ToMin Lin’, ‘To Max Lin’). In this situation, the preferred output torqueand the preferred battery power are the optimized output torque (‘To*’),the optimized battery power (‘P_(BAT)*’). Otherwise, the achievableranges for the output torque are based upon based upon the availablebattery power, depending on whether discharging, i.e., the positive rootcase, or charging, i.e., the negative root case, and the linear torqueconstraints.

FIG. 7 depicts battery power (‘P_(BAT)’) plotted as a function of outputtorque (‘To’) for the exemplary powertrain system. The minimum andmaximum available battery power (‘P_(BAT) _(—) _(MIN)’ and ‘P_(BAT) _(—)_(MAX)’) are shown. The preferred output torque (‘To Opt’), describedhereinabove with reference to FIGS. 4 and 5 comprises the output torquethat is less than the immediate accelerator output torque request andyields the minimum battery power subject to and limited by the outputtorque constraints. The minimum available battery power comprises amaximum charging battery power for the ESD 74 in one embodiment. Thus,as depicted, the preferred output torque is based upon a capacity of thepowertrain to transmit tractive torque input from the driveline 90 tothe transmission 10, transfer the tractive torque via one or more of thetorque transfer clutches to spin one of the first and second electricmachines 56 and 72 which can be controlled to react the tractive torqueand transform it to electric power that is storable in the ESD 74. Thepreferred output torque is limited by the immediate or present torque,speed, and reactive clutch torque constraints, and electric power inputsthereto, described with reference to FIGS. 4 and 5. The operator torquerequests, including the immediate accelerator output torque requestconstrained (‘To Req Accel Cnstrnd’) can be similarly plotted. Thepreferred regenerative braking capacity (‘Opt Regen Capacity’) i.e., thepresent torque capacity of the transmission 10 to react tractive torquecomprises an output torque range between the preferred output torque andthe immediate accelerator output torque request. The preferredregenerative braking capacity (‘Opt Regen Capacity’) is a permissibleoutput torque operating range. Thus, the output torque is constrainedwithin the preferred regenerative braking capacity, and the output andmotor determination scheme 340 controls operation of the first andsecond electric machines 56 and 72 to achieve the output torque,including during shifts in the operating range state.

It is understood that modifications are allowable within the scope ofthe disclosure. The disclosure has been described with specificreference to the preferred embodiments and modifications thereto.Further modifications and alterations may occur to others upon readingand understanding the specification. It is intended to include all suchmodifications and alterations insofar as they come within the scope ofthe disclosure.

1. Method for operating a hybrid powertrain system including atransmission operative to transfer power between an input member and atorque machine and an output member coupled to a driveline coupled to awheel including an actuable friction brake, the torque machine operativeto react torque transferred from the wheel through the driveline to theoutput member of the transmission, the torque machine connected to anenergy storage device, the method comprising: monitoring an operatortorque request input to an accelerator pedal; determining a minimumavailable power output of the energy storage device; determining apreferred output torque reacted through the output member to thedriveline based upon the minimum available power output of the energystorage device; determining a regenerative braking torque capacitycomprising a torque range between the preferred output torque reactedthrough the output member to the driveline and the operator torquerequest input to the accelerator pedal; and controlling operation of thehybrid powertrain based upon the regenerative braking torque capacity.2. The method of claim 1, further comprising: determining an immediateaccelerator output torque request based upon the operator input to theaccelerator pedal; and determining the regenerative braking torquecapacity based upon the preferred output torque reacted through theoutput member to the driveline and the immediate accelerator outputtorque request.
 3. The method of claim 2, wherein the minimum poweroutput from the energy storage device comprises a maximum charging powerfor charging the energy storage device at a powertrain system operatingpoint.
 4. The method of claim 1, further comprising determining thepreferred output torque reacted through the output member to thedriveline based upon the minimum available power output of the energystorage device and torque constraints on the hybrid transmission.
 5. Themethod of claim 4, wherein the minimum available power output of theenergy storage device comprises a maximum charging power.
 6. The methodof claim 1, further comprising monitoring operator input to a brakepedal and determining an immediate brake output torque request basedupon the operator input to the brake pedal during an operator brakerequest; and controlling torque output of the power generating devicebased upon the immediate brake output torque request and the preferredregenerative braking capacity.
 7. The method of claim 1, furthercomprising selectively applying torque transfer clutches of thetransmission to transfer power between the torque machine and the outputmember in one of fixed gear and continuously variable operating rangestates.
 8. The method of claim 7, further comprising: commanding a shiftfrom the fixed gear operating range state including operating in thecontinuously variable operating range state; and controlling outputtorque from the transmission in the continuously variable operatingrange state based upon the regenerative braking torque capacity.
 9. Themethod of claim 7, further comprising determining the preferred outputtorque reacted through the output member to the driveline based upon theminimum available power output of the energy storage device and a clutchreactive torque for the selectively applied torque transfer clutch. 10.Method for operating a hybrid powertrain system including a transmissionoperative to transfer power between an input member and a plurality oftorque machines and an output member coupled to a driveline coupled to awheel including an actuable friction brake, one of the torque machinesoperative to react torque transferred from the wheel through thedriveline to the output member of the transmission, the torque machinesare connected to an energy storage device; the method comprising:monitoring an operator torque request input to an accelerator pedal;determining a minimum available power output of the energy storagedevice; determining a preferred output torque reacted through the outputmember to the driveline based upon the minimum available power output ofthe energy storage device; determining a regenerative braking torquecapacity comprising a torque range between the preferred output torquereacted through the output member to the driveline and the operatortorque request input to the accelerator pedal, and controlling operationof the hybrid powertrain based upon the regenerative braking torquecapacity.
 11. The method of claim 10, further comprising selectivelyapplying torque transfer clutches of the transmission to transfer powerbetween the torque machines and the output member in one of fixed gearand continuously variable operating range states.
 12. The method ofclaim 11, further comprising: commanding a shift from one of the fixedgear operating range states including operating in the continuouslyvariable operating range state; and controlling output torque from thetransmission in the continuously variable operating range state basedupon the regenerative braking torque capacity.
 13. The method of claim12, further comprising: commanding a shift from the fixed gear operatingrange state including operating in the continuously variable operatingrange state; and controlling output torque from the transmission in thecontinuously variable operating range state based upon the regenerativebraking torque capacity.
 14. The method of claim 13, further comprisingdetermining the preferred output torque reacted through the outputmember to the driveline based upon the minimum available power output ofthe energy storage device and clutch reactive torque for the selectivelyapplied torque transfer clutch.
 15. The method of claim 14, comprisingdetermining motor torque commands for controlling the torque machinesbased upon the preferred output torque reacted through the output memberto the driveline.
 16. Method for operating a hybrid powertrain systemincluding a transmission operative to transfer power between an inputmember and a plurality of torque machines and an output member coupledto a driveline coupled to a wheel, the transmission operative totransfer power between the input member and the torque machines and theoutput member in one of a fixed gear and a continuously variableoperating range state through selective actuation of torque transferclutches, the torque machines are connected to an energy storage device,and one of the torque machines operative to react torque transferredfrom the wheel through the driveline to the output member of thetransmission, the method comprising: monitoring an operator torquerequest input to an accelerator pedal; determining a minimum availablepower output of the energy storage device; determining a preferredoutput torque reacted through the output member to the driveline basedupon the minimum available power output of the energy storage device;determining a regenerative braking torque capacity comprising a torquerange between the preferred output torque reacted through the outputmember to the driveline and the operator torque request input to theaccelerator pedal; and controlling operation of the hybrid powertrainbased upon the regenerative braking torque capacity.
 17. The method ofclaim 16, further comprising: commanding a shift from one of the fixedgears including operating in the continuously variable operating rangestate; and controlling output torque from the transmission in thecontinuously variable operating range state based upon the regenerativebraking torque capacity.
 18. The method of claim 17, further comprisingdetermining the preferred output torque reacted through the outputmember to the driveline based upon the minimum available power output ofthe energy storage device and clutch reactive torque for the selectivelyapplied torque transfer clutch.
 19. The method of claim 18, comprisingdetermining motor torque commands for controlling the torque machinesbased upon the preferred output torque reacted through the output memberto the driveline.